1. Field of the Invention
The present invention relates to a servo signal recording method for recording a servo signal on a magnetic recording medium having a servo band. The present invention also relates to a servo recording apparatus capable of recording a servo signal on a magnetic recording medium. The present invention also relates to a magnetic recording medium on which a servo signal is recorded by a servo signal recording method or a servo signal recording apparatus.
2. Description of Related Art
A magnetic tape that is a kind of magnetic recording medium finds various applications such as an audio tape, a video tape, and a computer tape. Particularly, in the field of a tape for a data backup in a computer, tapes with a storage capacity of hundreds of gigabytes per volume have been commercialized along with the increase in capacity of a hard disk in which a backup is to be created. In the future, the increase in capacity of a backup tape is indispensable for dealing with the further increase in capacity of a hard disk. Along with the increase in capacity, there is a demand for high-density recording. For this purpose, a magnetic layer is reduced in thickness, which may decrease the output level of a servo signal.
Conventionally, there is a method for substantially doubling the output level of a servo signal by DC(direct current)-erasig a magnetic tape before recording a servo signal on the magnetic tape so as to enhance the output level of a servo signal (see JP 8(1996)-30942 A). According to this method, if the magnetic tape is magnetized (DC-erased) with one polarity, a servo pattern during recording of a servo signal is composed of magnetic flux transition between magnetization areas with opposite polarities. FIG. 6(a) shows characteristics of a servo signal read from an AC(alternating current)-erased magnetic tape. FIG. 6(b) shows characteristics of a servo signal read from a DC-erased magnetic tape. As shown in FIG. 6(b), the amplitude of the servo signal read from the DC-erased magnetic tape is about twice (2Vo) the amplitude Vo of the servo signal shown in FIG. 6(a).
Furthermore, JP 2005-63623 A discloses a method for controlling DC erasure by providing a DC erasing head with an azimuth, and controlling the output level of a servo signal by operating a DC component.
However, according to the method disclosed by JP 8(1996)-30942 A, there is a problem that the output level of a servo signal cannot be controlled since the output level of a servo signal is fixed at 2Vo. For example, according to a linear tape open (LTO) specification, a signal output level capable of being reproduced for each recording and reproducing apparatus is determined as a specification, which may cause the following possibility: when the reproduction output level of a servo signal is too high, a magnetic head is saturated, and when the reproduction output level of a servo signal is too low, a signal/noise (S/N) ratio of the servo signal cannot be taken, and in any case, a servo signal cannot be reproduced normally. Thus, although it is necessary to control the output level of a servo signal in accordance with the specification, the output level of a servo signal cannot be controlled by the method of JP8(1996)-30942 A, so that a servo signal may not be reproduced normally.
Furthermore, according to the configuration disclosed by JP 8(1996)-30942 A, since a data track as well as a servo track are DC-erased, there is a problem that the S/N ratio of data recorded on the data track may be decreased.
Furthermore, according to the method disclosed by JP 2005-63623 A, the configuration of rotating a DC erasing head is required, which causes a problem that a servo signal recording apparatus is enlarged.